Human vision may be capable of appreciating contrast ratios of up to 1:10,000 or more. Most conventional digital image formats (so-called 24-bit formats) use up to 24 bits to store both color and luminance information for each pixel in an image. Such formats may be called “output referred standards” because they do not attempt to preserve image information beyond what could be reproduced by legacy electronic displays of the types most commonly available in the past.
Display technologies being developed by the assignee, and others, are able to reproduce images having high dynamic range (HDR). Such displays can reproduce images that more faithfully represent real-world scenes than conventional displays.
To support backwards compatibility as well as new HDR display technologies, an HDR image may be represented by a tone-mapped image with additional metadata. On one hand, the tone-mapped image is used to present a normal dynamic range image (e.g., on a legacy display). On the other hand, the additional metadata may be used with the tone-mapped image to generate, recover, or present a HDR image (e.g., by a HDR display).
A few different tone mapped operators (TMOs) might be used to create tone-mapped images based on HDR images. Among these TMOs, the Reinhard global photographic operator is used to produce tone-mapped images relatively efficiently. However, the Reinhard operator suffers from the shortcoming of losing a relatively large amount of image details, particularly in bright areas. The bilateral filter is used to produce relatively high quality tone-mapped images. However, the computation cost for the bilateral filter is very high, possibly, sixty times of relatively simple TMOs such as the Reinhard operator. Other TMOs such as the histogram adjustment operator or the gradient domain operator were found not to work as well as those mentioned above.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. Similarly, issues identified with respect to one or more approaches should not assume to have been recognized in any prior art on the basis of this section, unless otherwise indicated.